I'll deal with the plastic ones. I've had metal, steel, which was the standard. I protected the base rim with the car door stick on silver edging, tried to keep them clean but they too failed although in different ways. And they left rust stains and damaged things if you set them down a bit too hard.
So although I think the plastic tank/jerry can manufacturers can do better I'll curse at the splits but continue with them.
To me the shapes of the plastic tank is easier to find stowage for.